1. Field of the Invention
The present invention relates to a laser beam optical scanning device, and more specifically relates to a laser beam optical scanning device which deflection scans a unidirectional laser beam emitted from a light source within a single plane by a deflection assembly, so as to write an image on the surface of a photosensitive member.
2. Description of the Related Art
In recent years, laser printers have been developed which use laser beam optical scanning devices providing a laser generating section, a laser beam deflection scanning section, and image forming optical elements integratedly incorporated within a housing to accomplish the scanning exposure of an image on the surface of a photosensitive member. The aforesaid optical device comprises a single unit and is independent of other parts of the laser printer, and has become widely used particularly in a compact laser printer because said optical device is easily adjustable during manufacture as well as easily maintained.
A common problem heretofore is soiling of the print head and the resultant defects of the reproduced image. Some cause of said print head soiling have been overlooked, including, from the perspective of the construction of the electrophotographic system, the residual toner remaining in the vicinity of the print head, and foreign matter which adheres to the print head during assembly or adjustment operations (e.g., mainly human hair of the technicians). Furthermore, human hair of an operator occasionally adheres to the print head or in the vicinity thereof during routine maintenance and paper jam processing.
That is, residual toner particles (several tens of microns in diameter) remains in the laser beam emitting section and are flow from the emission aperture into the print head in the air currents generated via the rotation of the polygonal mirror, thereby soiling the optical elements. A transparent glass plate may be mounted on the aforesaid emission aperture to prevent the previously described airborne flow of toner particles.
The previously described airborne flow of toner particles into the print head is prevented when a glass plate is provided on the emission aperture, however, such an arrangement has the disadvantage in allowing toner particles, hair and the like to adhere to the exterior side of said glass plate. In particular, the adherence of hair, which has a large shielding area compared to that of toner particles, directly affects image loss.